U.S. patent application number 10/043384 was filed with the patent office on 2002-09-12 for sub- field driven display device and method.
Invention is credited to Holtslag, Antonius Hendricus Maria, Van Dijk, Roy.
Application Number | 20020126070 10/043384 |
Document ID | / |
Family ID | 8172199 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020126070 |
Kind Code |
A1 |
Holtslag, Antonius Hendricus Maria
; et al. |
September 12, 2002 |
Sub- field driven display device and method
Abstract
The present invention provides for a sub-field driven display
device and related method wherein sub-fields are weighted and
duplicated for achieving a plurality of grey levels by way of a
plurality of sub-fields, and in which the sub-fields are weighted
as a ternary distribution of sub-field weights.
Inventors: |
Holtslag, Antonius Hendricus
Maria; (Eindhoven, NL) ; Van Dijk, Roy;
(Eindhoven, NL) |
Correspondence
Address: |
Michael E. Marion
U.S. Philips Corporation
580 White Plains Road
Tarrytown
NY
10591
US
|
Family ID: |
8172199 |
Appl. No.: |
10/043384 |
Filed: |
October 26, 2001 |
Current U.S.
Class: |
345/60 |
Current CPC
Class: |
G09G 2320/0261 20130101;
G09G 3/2803 20130101; G09G 3/2029 20130101; G09G 2320/0266
20130101 |
Class at
Publication: |
345/60 |
International
Class: |
G09G 003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2000 |
EP |
00203787.7 |
Claims
1. A sub-field driven display device (10) having a sub-field
converter (18) for converting video signals into sub-field data in
which the sub-fields are weighted and duplicated for achieving a
plurality of grey levels by way of a plurality of sub-fields,
characterized in that the sub-field converter (18) is arranged to
weight the sub-fields as a ternary distribution of sub-field
weights.
2. A display device (10) as claimed in claim 1, wherein the
sub-field converter (18) is arranged to employ symmetrical
duplicated ternary weights.
3. A display device (10) as claimed in claim 1 or 2, wherein the
sub-field converter (18) is arranged to distribute the ternary
weights in a manner of increasing weighted value toward a central
value or values.
4. A display device (10) as claimed in claim 1, 2 or 3, wherein the
sub-field converter (18) is arranged to provide the highest
sub-field weight at the centre of the ternary distribution.
5. A display device (10) as claimed in any one of claims 1 to 4,
and including motion compensation means employing motion estimation
serving to enhance motion artefact reduction.
6. A display device (10) as claimed in any one of claims 1 to 5,
wherein the sub-field converter (18) is arranged to alternate light
output control patterns in predetermined units of the display.
7. A display device (10) as claimed in claim 6, wherein the pattern
comprises a checker-board pattern.
8. A method of driving a display device (10) by means of a
plurality of weighted and duplicated sub-fields, characterized by
the step of weighting the sub-field in accordance with a ternary
distribution of weights.
9. A method as claimed in claim 8, and employing symmetrical
duplicated ternary weights.
10. A method as claimed in claim 8 or 9, wherein the ternary
weights are distributed in a manner of increasing weighted value
toward a central value or values.
11. A method as claimed in any one of claim 8, 9, or 10, wherein
the highest sub-field weight is found in the centre of the ternary
distribution.
12. A method as claimed in any one of claims 5 to 11, and including
the step of duplicated sub-field addressing.
13. A method as claimed in claim 12, and including motion
compensation employing motion estimation serving to enhance motion
artefact reduction.
14. A method as claimed in claim 12 or 13, and including the step
of alternating light output control patters in predetermined units
of the display.
15. A method as claimed in claim 14, wherein the pattern comprises
a checker board pattern.
Description
[0001] The present invention relates to a sub-field driven display
device and method wherein sub-fields are weighted and duplicated
for providing a plurality of grey levels by way of a plurality of
sub-fields.
[0002] Such a sub-field driven display and method are known from
EP-A-0 896 317 which discloses a colour image display device
wherein colour video signals are supplied to red, green and blue
light-emitting cells, for example, the cells of a plasma display
device. The device employs the known sub-field method of displaying
the required grey scale representation by controlling the
light-emitting luminous levels of the respective red, green and
blue light-emitting cells. In this known sub-field method, one
display field is divided into a plurality of sub-fields on a time
base and light-emitting weights are allotted to the respective
sub-fields, and light emission in each of the respective sub-fields
is then either controlled in an on/off manner so as to provide the
appropriate grey level gradation. The required gradation is
commonly provided by employing a binary ratio weighting for the
sub-fields.
[0003] Performance can be disadvantageously limited with such known
display devices and methods and the present invention seeks to
provide for a sub-field driven display device and method offering
improved performance. In particular the present invention seeks to
provide improved performance through the identification of
particular limitations, and related problems, as found in the prior
art and which are identified in accordance with the present
invention and arise particularly in view of the number of
sub-fields employed, which serves to disadvantageously limit the
performance of known devices and methods due to motion artefacts
and the limited number of grey levels available.
[0004] The present invention further seeks to provide for an
improved sub-field driven display device and method which readily
allows for the adoption of duplicated sub-field addressing.
[0005] According to one aspect of the present invention, there is
provided a sub-field driven display device of the type defined
above, characterized in that the sub-fields are weighted in
accordance with a ternary distribution of sub-field weights.
[0006] As will be illustrated further within the present
application, the adoption of a ternary distribution of weights
advantageously optimizes the ratio of grey levels to sub-fields
adopted such that, when compared with known weighting
distributions, and for a given number of sub-fields, the present
invention advantageously allows for an increased number of grey
levels, thereby advantageously enhancing the performance of
sub-field driven display devices. Stated in the alternative, the
invention therefore has the advantage that, with a minimal number
of sub-fields, the highest maximum value of grey level can be
achieved while still retaining the possibility of also producing
all intermediate grey level values.
[0007] The feature defined in claim 2 is particularly advantageous
in readily allowing for the application of a duplicated sub-field
addressing method which, in turn, advantageously reduces motion
artefact problems that can be apparent in such devices.
[0008] The feature of claim 3 further facilitates such advantages
and the feature defined in claim 4 has the advantage that, with the
heaviest weighting value found within the middle of the sub-field
weighting distribution, this central sub-field position can
advantageously act as a reference time value for motion
compensation.
[0009] The features defined in claims 5 to 8 relate to
corresponding method steps for the present invention and exhibit
advantages similar to those discussed above.
[0010] The feature defined in claim 9 specifically introduces the
adoption of a duplicated sub-field addressing method which can
readily be achieved in accordance with the sub-field distribution
arising in the present invention. Such an addressing method allows
for motion artefact reduction, even without use of a motion
estimator, and even though the method, if required, can be combined
with motion compensation based on motion estimation.
[0011] The present invention is described further hereinafter by
way of example only, with reference to the accompanying drawings in
which:
[0012] FIG. 1 represents a block diagram of a display device
embodying the present invention; and
[0013] FIG. 2 comprises a tabular representation grey level
production for two pixels in accordance with an embodiment of the
present invention.
[0014] It should be appreciated that the present invention can
readily employ the techniques for weighting and distributing
duplicated sub fields as disclosed in EP-A-0 899 710, EP-A-0 698
874 and EP-A-0 896 317.
[0015] As will be appreciated, the present invention relates to the
adoption of a ternary weighting distribution for a sub-field driven
display device and related method in which, as will be illustrated
below, specific advantages leading to an improved performance in
display devices can be achieved.
[0016] For example, the ternary distribution:
[0017] 1,3,9,27,9,3,1
[0018] represents a particularly advantageous weighting in
accordance with the present invention since the ternary
distribution is not only a symmetrical distribution but also offers
its maximum value at the centre of the distribution.
[0019] As will be appreciated, through the effective use of seven
sub-fields--each--employing a respective one of the weightings
noted above all integer values of grey level between 0 and the
maximum possible grey level, 53 in this example, can be realised.
When compared, for example, with a binary distribution as known in
the prior art, a greater number of sub-fields will be required in
order to arrive at a similar number of grey level values. This is
particularly true for symmetrical series.
[0020] The ternary distribution has associated advantages in that
it readily allows for particularly effective motion artifact
reduction through the application of the known duplicated sub-field
addressing method which, if required, can be combined with motion
compensation based on motion estimation.
[0021] As noted in the above example, it is particularly
advantageous to provide for the heaviest weighting value in the
centre of the sub-field weighting distribution since this sub-field
position can then readily act as a reference time t=0, for motion
compensation. This can be preferred since the maximum amount of
light is generated within the middle of the sub-field distribution
and is not liable to be effected by any possible truncation error.
The lower weights, i.e. the weighting values of the sub-fields on
either side of the central heaviest weight, are then effectively
duplicated on either side of the central weight and turned on in
accordance with the example of two driven pixels as illustrated in
the accompanying drawing.
[0022] Turning now to FIG. 1, there is illustrated in
block-diagrammatic form one embodiment of a display device 10
according to the present invention. The device 10 includes
analog/digital converters 12, 14, 16 for each of the incoming
analog Red, Green and Blue video signals, which converters
subsequently supply the digital video signals to a sub-field
converter 18. The signals output from the sub-field converter 18
are received by a sub-field sequence converter 20 including a frame
memory which in turn supplies the sub-field divided signal to a
display driver 22. The driver 22 is arranged to provide drive
signals to the display such as a plasma display panel 24.
[0023] Referring now to the drawing, shown in FIG. 2, each of the
possible 18 grey levels is identified down the left-hand column
whereas the ternary weighting for each of the 5 sub-fields of each
of pixels 1 and 2 is illustrated across the top row of the table
and confirms that the ternary distribution 1,3,9,3,1 is employed
for illustrative purposes within this embodiment of the present
invention. The distribution of crosses within the table indicates
which of the weighted sub-fields is driven in order to provide the
particular grey scale level indicated in the left-hand column.
[0024] In further detail, consideration can be given to the
distribution of (2n+1) values a.sub.i:
[0025] a.sub.0, a.sub.1, a.sub.2, a.sub.3, . . . , a.sub.n-1,
a.sub.n, a.sub.n-1, . . . , a.sub.3, a.sub.2, a.sub.1, a.sub.0,
while a.sub.0=1
[0026] With a number of grey levels, G.sub.2n+1, equal to (note:
consider also the grey value 0): 1 G 2 n + 1 = 1 + a n + 2 0 n - 1
a i
[0027] The symmetrical distribution is constructed in order to
apply the distributed sub-field method. The values a.sub.n are
integer values, such that all values from 0 to G.sub.2n+1 can be
realised.
[0028] The heaviest weights will preferably be in the middle of the
distribution, while the smaller values are located further away
from the middle; therefore a.sub.0=1.
[0029] A distribution for n=4 is advantageously constructed as
follows:
1 a.sub.0 a.sub.1 a.sub.2 a.sub.3 a.sub.4 a.sub.3 a.sub.2 A.sub.1
a.sub.0 Construction comment: 1 . . . . . . . . . . . . . . . . . .
. . . 1 sum 2, so take 3 as next DSF number 1 3 . . . . . . . . . .
. . . . . 3 1 sum 8, so take 9 as next DSF number 1 3 9 . . . . . .
. . . 9 3 1 sum 26, so take 27 as next DSF number 1 3 9 27 81 27 9
3 1 sum 80, finalise with 81 in the middle
[0030] Thus all integer values between 0 and a maximum grey level
of 161 can be produced giving G.sub.9=162 grey levels.
[0031] In general: a.sub.n=3.sup.n, n=0, 1, 2, 3 . . . ,
[0032] Giving: 2n+1 sub-fields,
[0033] While: G.sub.2n+1=2.3.sup.n.
[0034] This provides for a ternary series.
[0035] For a symmetrical binary series of (2n+1) sub-fields, with
the highest weight in the middle, the number of grey levels equals
G.sub.2n+1=2.2.sup.n, which is a factor (3/2).sub.n less. At
(2n+1)=9 sub-fields (thus n=4), this differs a factor 5.0625 (5).
This clearly illustrates how, for a given number of sub-fields the
device and method of the present invention can provide for an
optimum number of grey scale values.
[0036] At an even number of sub-fields, one additional term is
generally to be determined. To keep the distribution fully
symmetrical, the heaviest weight can be copied, or repeated, in the
middle as follows:
[0037] a.sub.0, a.sub.1, a.sub.2, a.sub.3, . . . , a.sub.n-1,
a.sub.n, a.sub.n, a.sub.n-1, . . . , a.sub.3, a.sub.2, a.sub.1,
a.sub.0, while a.sub.0=1
[0038] example for n=3: 1,3,9,27,27,9,3,1, G.sub.8=81.
[0039] Alternatively, a series can be developed in which the term
ao is not duplicated. Using the same values as above, this arrives
at:
[0040] 1,2,6,18,54,18,6,2
[0041] which for the same number of eight sub-fields gives 108 grey
levels.
[0042] As will be appreciated, the maximum possible number of grey
levels is advantageously achieved in accordance with the present
invention while, if required, for the highest of all possible
weights, a symmetrical value can also be adopted. When also
applying the duplicate sub-field method so as to achieve motion
compensation, the pixels identified as A pixel and B pixel in the
duplicated sub-field method can advantageously be addressed by one
of the symmetrical options.
[0043] It should of course be appreciated that the present
invention can be used in all displays which employ sub-field
distributions and include, but are not limited to, Plasma Display
Panels, Digital Mirror Devices and Dynamic Foil Displays.
[0044] Also the invention is not restricted to the details of the
foregoing embodiment since, for example, an asymmetrical ternary
distribution, and without having the highest weighted value
centrally located, could still nevertheless advantageously be
employed so as to arrive at advantages offered by the present
invention.
* * * * *